Inverter Overvoltage: Causes & Solutions Explained

Overvoltage Fault Analysis in Inverter Voltage Detection

The inverter is the core of modern electric drive systems, enabling precise motor speed control. To ensure safe and stable operation, it continuously monitors key parameters—voltage, current, temperature, and frequency. This article analyzes overvoltage faults in inverter voltage detection circuits.

Inverter overvoltage refers to the DC bus voltage exceeding a safe threshold, risking component damage and triggering protective shutdown. Under normal operation, the DC bus voltage is the rectified and filtered average of the three-phase AC input. For a 380V AC supply, the theoretical DC bus voltage is:
Ud = 380V × √2 ≈ 537V.

During overvoltage events, the main DC bus capacitor charges and stores energy, causing voltage to rise. When it approaches the capacitor’s rated value (typically ~800V), the inverter activates overvoltage protection and shuts down. Failure to respond may lead to performance degradation or permanent damage.

Overvoltage faults are primarily caused by two factors:

1. Excessively High Input AC Voltage

Grid surges, transformer faults, incorrect cabling, or overvoltage from diesel generators can raise input voltage beyond allowable limits. In such cases, disconnect the power supply, identify and correct the fault, and restart only after voltage normalizes.

2. Regenerative Energy from the Load

Common in high-inertia systems, when the motor’s synchronous speed exceeds the inverter’s output speed, the motor acts as a generator, feeding energy back into the DC bus and causing voltage to rise.

Solutions include:

• Extend Deceleration Time: Slower deceleration prevents the motor from entering regenerative mode by keeping the inverter’s output frequency above the motor’s actual speed.

• Enable Overvoltage Stall Prevention: This function detects rising DC bus voltage and automatically slows the frequency ramp-down to avoid regeneration.

• Use Dynamic Braking (Braking Resistor): Dissipates regenerative energy as heat via an external resistor, limiting bus voltage rise.

• Additional Measures:

• Install a regenerative feedback unit to return energy to the grid.

• Use a common DC bus configuration: connect multiple inverters’ DC buses in parallel, allowing regenerating inverters to feed energy to motoring ones, stabilizing voltage.